Multilayer piezoelectric ceramic electronic components, such as multilayer piezoelectric actuators, offering a great displacement even at low voltage have been in growing demand in recent years.
The manufacture of a multilayer piezoelectric ceramic electronic component of this type usually involves alternately stacking piezoelectric ceramic layers and conductive layers as a precursor of inner electrodes and cofiring the obtained stack.
The inner electrodes are commonly made of Ag—Pd alloys, but Ag—Pd alloys are more expensive than non-precious metals. Furthermore, electronic components using such an alloy often experience electrochemical migration of Ag when operated in a low-frequency band or with DC voltage. It is therefore desirable to use a low-migration material.
In order for such electrochemical migration to be effectively prevented at low cost, it is preferred that the inner electrodes be made of a material based on Ni, a metal available at relatively low prices.
Ni is, however, easily oxidized when fired in an air atmosphere and needs to be fired in a reducing atmosphere. A piezoelectric material is therefore required that can be cofired in a reducing atmosphere.
As a solution to this, Patent Document 1 proposes a piezoelectric ceramic composition that contains a main ingredient represented by a general formula {(1−x)(K1-a-bNaLib) (Nb1-cTac)O3-xM2M4O3} (where M2 represents at least one of Ca, Ba, and Sr, M4 represents at least one of Zr, Sn, and Hf, and x, a, b, and c meet the following conditions: 0.005≤x≤0.1, 0≤a≤0.9, 0≤b≤0.1, 0≤a+b≤0.9, and 0≤c≤0.3) and 2 to 15 moles of Mn per 100 moles of the main ingredient, with the M4 content in the range of 0.1 to 5.0 moles per 100 moles of the main ingredient.
According to Patent Document 1, the above constitution makes a piezoelectric ceramic composition more sinterable in a reducing atmosphere, allowing the ceramic composition to be completely sintered even if cofired with a Ni-based inner electrode material in a reducing atmosphere. As a result, a piezoelectric ceramic electronic component is obtained with good piezoelectricity.    Patent Document 1: International Publication No. 2008/152851 (claims 1 and [0024])